1. Field of the Invention
The present invention relates to a process for production of methylnaphthalenes from a raffinate resulting from recovery of normal paraffins from a kerosene fraction.
2. Related Art Statement
Methylnaphthalenes can be used as solvent, dye-carrier, heat transfer medium and the like and besides reacted with methanol to produce 2,6-dimethylnaphthalene. This 2,6-dimethylnaphthalene is used as a starting material for production of polyesters such as polyethylene naphthalates and the like. These polyesters can be formed into synthetic fibers and films having excellent characteristics.
Methylnaphthalenes are contained in coal tar or cycle oils in a fluid catalytic cracking process, but these cycle oils contain a high concentration of contaminants such as sulfur and nitrogen compounds and so on.
By the way, when producing 2,6-dimethylnaphthalene which is the monomer of said polyesters, methylnaphthalene having a high purity, particularly a low concentration of the above-described contaminants is desired for the reason of deactivation of catalyst, inhibition of by-product, increase in yield and the like.
With respect to nitrogen compound among these contaminants, a process for eliminating it by acid, alkali cleaning or the like is performed. Further, with respect to sulfur compound, there is proposed a process for refining the oil by recrystallization, fusing crystallization or the like after heat-treating with anhydrous aluminum chloride (see JP-A-62-230736 and JP-A-62-230737 (the term "JP-A" as used herein means an "unexamined published Japanese patent application")).
In the process for cleaning the oil with acid and alkali, however, it is impossible to sufficiently eliminate the sulfur compound and also a problem is in the disposal of used acid and alkali.
On the other hand, even in the process for refining the oil with anhydrous aluminum chloride, it is impossible to decrease the sulfur compound content to the extent that the deactivation of catalyst can sufficiently be inhibited and also a problem is in the waste disposal.
Further, when directly subjecting coal tar, cycle oils in a fluid catalytic cracking process or fractions thereof to a hydrorefining process in order to eliminate the above-described contaminants, the hydrogenation of the nucleuses of methylnaphthalenes can not be avoided, resulting in a great reduction in yield of methylnaphthalenes. Therefore, additional dehydrogenation is needed and a problem arises in that the production cost is markedly increased.
Normal paraffins are recovered from a kerosene fraction as a starting material for production of linear alkylbenzene sulfonates (LAS) as synthetic detergents, and the like, but the remaining raffinate after recovery of normal paraffins has a comparatively high smoking point and thus is not preferred as a fuel kerosene.
The inventors have made various investigations in order to solve such problems and as a result found that a product oil obtained by reforming reaction of a particular fraction of the above-described raffinate contains a large amount of methylnaphthalenes, from which can be recovered methylnaphthalenes having such a high purity that they are almost free from nitrogen and sulfur compounds by separation.
Incidentally, it is reported that catalytic reforming of a kerosene fraction provides heavy aromatic compounds and that the heavy aromatic compounds contain methylnaphthalenes (Sekiyu Gakkaishi, Vol. 13, No. 6 (1970), pp. 468-474). But, it has astonishingly been found that the reforming reaction of a particular fraction of the raffinate results in a great increase in an amount of the resulting methylnaphthalenes, as compared with the reforming reaction of the kerosene fraction. The present invention is based on such a discovery.